In many industrial processes, liquid and gas mixtures have to be phase separated in order to remove liquid droplets from gas streams to satisfy environmental standards (e.g., radioactive water from steam at nuclear power plants) or to purify gas streams, increase liquid recovery, and to protect rotating equipment located downstream (e.g., oil processing facilities, engine air intakes, gas processing plants). A complete phase separation will eventually occur without employing any mechanical devices given long contact times; however to accelerate this process several separation techniques have been proposed. These techniques operate based on one or more physical forces accelerating fluid separation, such as inertial, gravitational, diffussional, centrifugal and electrostatic. Mechanical equipment operating on these principles include impingement separators (baffle, wire mesh, vanes), as described in U.S. Pat. Nos. 3,938,972, 3,965,005, and 4,668,256, cyclones, as described, for example, in U.S. Pat. No. 3,979,392, knock-out pots, and filters, as described in U.S. Pat. Nos. 4,938,869 6,017,377, and 7,309,367, and wet precipitators, as described in U.S. Pat. No. 5,843,210.
The above separation techniques are selected based on the liquid collection efficiency requirement, gas flow rate and liquid loading, solid deposition tolerance, pressure drop, and capital cost. There is a need to develop liquid/gas separators that will achieve high level of liquid removal efficiency and throughput and at the same time minimize the amount of energy that is required to treat the gas (pressure drop) and minimize capital cost.
One of the most widely used gas/liquid separators are impingement separators. The basic elements of impingement separators are strategically located devices (targets) on which liquid droplets collide. The simplest impingement separators consist of a baffle or disk inserted against the vessel inlet. These separators provide low droplet removal efficiency but can remove bulk of the liquid entering the vessel. To improve efficiency and recovery of smaller droplets more sophisticated impingement separators have been developed. One type of these devices is vane-type separator that consists of parallel plates (see, e.g., U.S. Pat. Nos. 3,813,855, 4,581,051 and 4,557,740) that are straight or bent creating flow channels. Typically, the channels are of uniform cross section across their entire length (see, e.g., U.S. Pat. No. 5,972,062). In these devices, liquid droplets present in the gas stream impinge on the plates due to inertia of the droplets and collect on the vane surfaces in the form of a film of liquid. This liquid film (recovered liquid) drains down the vane into the collection devices without re-entrainment. The channels also can be arranged radially using serpentine vanes (see, e.g., U.S. Pat. No. 5,112,375).
Different arrangements of vanes are described in the open literature (see, e.g., Perry's Chemical Engineers' Handbook, Sixth Edition, McGraw-Hill, 1984, p. 18-74). In some applications vanes consist of flat plates bent at predetermined angle assembled parallel typically in a zig-zag fashion (see, e.g., U.S. Pat. Nos. 5,464,459 and 4,601,731). To increase liquid removal efficiency, vanes can be equipped with strategically located pockets that extend into the gas stream. Several patents disclose single and double vane pockets (see e.g., U.S. Pat. Nos. 6,852,146, 5,268,001 and 5,104,431). In both cases, pockets increase vane efficiency (liquid removal efficiency) either by increasing turbulence (single pockets) or improving gas dynamics (double pockets). The vanes can be arranged in a multi-pass arrangement (see, e.g., U.S. Pat. No. 6,083,302).
Regardless of the vane arrangement, a breakthrough point exists where liquid droplets will leave the separator if fluid velocity exceeds its critical value (typically empirically determined maximum allowed velocity) defined as fluid flow (standard cubic feet per minute, SCFM) divided by vane cross-sectional area (square feet). Such determined fluid velocity can be employed to determine fluid dynamic pressure (ρV2) that includes effects of fluid density. For a given fluid flow, in order to maintain fluid velocities or dynamic pressure values below critical values, the cross-sectional area of the vane is increased until velocity falls below its critical value. Unfortunately, such an increase of vane dimensions results not only in additional capital cost required to fabricate larger vanes, but also corresponding increase of the vane containing vessel dimensions that additionally greatly increases capital costs. Of course, a vane that would be capable of increasing allowable velocity without performance deterioration or the vane that would increase liquid removal efficiency without increasing vane dimensions would be beneficial considering technical and economical factors.